I. Develop and apply impage magnifier microradiographic technique to study tooth sections, both enamel and dentin, under demineralizing and remineralizing conditions. Conventional X-ray sources as well as high energy synchrotron radiation will be used in these studies. With the use of synchrotron radiation, this technique can be used for (i) quantitative assessment of the mineral loss or gain as functions of experimental conditions and time and (ii) for detection of morphological changes in the subsurface lesions and intact layer. II. Crystal chemistry of hydroxyapatite, octacalcium phosphate, and products derived by hydrolysis or, dehydration or, reaction with, or combination with octacalcium phosphate: The objective is to establish compositions, solubilities, mechanisms of growth and hydrolysis, and chemical relationships between the various products involved in biomineralization. The effects of pH, temperature and the presence of various inorganic ions and surface active biomolecules will be studied. The benefits will include better understanding of the structure and chemical properties of non-stoichiometric bioapatites, roles of octacalcium phosphate-organic molecule adducts, and the mechanisms of biomineralization processes. III. Crystal structures of compounds of interest to dentistry: Single-crystal X-ray and neutron diffraction techniques will be used. Also, the neutron powder diffraction profile analysis (Rietveld) will be used for the study of compounds which cannot be grown to a size for single crystal analysis and when the structure is partially known. The benefits include a better understanding of the structures, properties and mechanisms of formation of biominerals. IV. Develop slurries for remineralizing tooth surfaces and to improve the properties and methods of delivery of the calcium phosphate setting cement for specific clinical applications, such as root canal filler, bone implants, etc. The benefits include techniques to reverse the formation of dental caries and new materials for restorative dentistry.